            :times-solved 0
            :description "Two numbers are coprime if their greatest common divisor equals 1.  Euler's totient function f(x) is defined as the number of positive integers less than x which are coprime to x.  The special case f(1) equals 1.  Write a function which calculates Euler's totient function."
            :tags ["medium"]
+	   :approved true
            :tests ["(= (__ 1) 1)"
 		   "(= (__ 10) (count '(1 3 7 9)) 4)"
 		   "(= (__ 40) 16)"

           :times-solved 0
           :description "A <a href=\"http://en.wikipedia.org/wiki/Tic-tac-toe\">tic-tac-toe</a> board is represented by a two dimensional vector. X is represented by :x, O is represented by :o, and empty is represented by :e.  A player wins by placing three Xs or three Os in a horizontal, vertical, or diagonal row.  Write a function which analyzes a tic-tac-toe board and returns :x if X has won, :o if O has won, and nil if neither player has won."
           :tags ["medium" "game"]
           :tests ["(= nil (__ [[:e :e :e]\n            [:e :e :e]\n            [:e :e :e]]))"
		   "(= :x (__ [[:x :e :o]\n           [:x :e :e]\n           [:x :e :o]]))"
		   "(= :o (__ [[:e :x :e]\n           [:o :o :o]\n           [:x :e :x]]))"

           :times-solved 0
           :description "Given a string of comma separated integers, write a function which returns a new comma separated string that only contains the numbers which are perfect squares."
           :tags ["medium"]
	   :approved true
           :tests ["(= (__ \"4,5,6,7,8,9\") \"4,9\")"
		   "(= (__ \"15,16,25,36,37\") \"16,25,36\")"]}) 

